Updating or removing a local game rewrites its on-disk files. Peers that
were mid-download of that game would keep streaming bytes from files that
are being deleted or replaced, handing them a corrupt or stale copy.
There was also no authoritative notion of which game version a peer
should serve or accept, so a peer could serve whatever happened to be on
disk and downloaders could aggregate files from peers running mismatched
versions.
This introduces a reader-writer coordination scheme between outbound file
transfers (readers) and local mutation operations (writers), and gates
both serving and downloading on an authoritative game catalog version.
Reader-writer coordination:
- Track active outbound transfers per game in a shared `OutboundTransfers`
map of (id, CancellationToken), threaded through `Ctx`/`PeerCtx` and
registered by a `TransferGuard` in the stream service. The guard is
registered *before* the serve-eligibility check to close a TOCTOU window
where a writer could miss an in-flight reader.
- `stream_file_bytes` now honors a cancellation token at every await point
(file read, network send, stream close) via `tokio::select!`, so a
transfer aborts promptly instead of hanging on a stalled receiver.
- `begin_operation` marks a game active first, then cancels its outbound
transfers and waits for the count to reach zero before any
Updating/RemovingDownload work touches the filesystem.
- Active games are now hidden from library snapshots entirely while an
operation is in flight, instead of freezing their last announced state,
so peers stop discovering a game that is being mutated.
Authoritative version catalog:
- Replace the `HashSet<String>` catalog with `GameCatalog`, mapping each
game id to its expected version (from the bundled game.db / ETI data).
- Serving requires the local `version.ini` to match the catalog version
(`local_download_matches_catalog`); peer selection, file aggregation,
and majority size validation all filter on the expected version
(`peers_with_expected_version`, `aggregated_game_files`, and friends).
User-visible changes:
- The GUI shows confirmation dialogs before Update and Remove, and
surfaces a sharing-status indicator on game cards and the detail modal.
- A new `OutboundTransferCountChanged` event lets the UI reflect live
outbound transfer activity.
Test Plan:
- just test
- just frontend-test
- just clippy
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